The present invention relates to an impact type flow meter for measuring and controlling a flow rate of a particulate material such as cereal, and in particular to a flow meter utilizing a slanting or inclined detection plate.
The term "particulate material" used herein means not only a granular or particulate material but also a powdery or pulverulent material.
A conventional impact type flow meter is so constructed as to cause particulate material to drop onto an impact plate or detection plate and to calculate a flow rate thereof from its impact force. The detection plate is mounted with an inclination or descent so that the particulate material impinging thereupon can slide down at once with no stagnation. Such a flow meter is seen in, for example, U.S. Pat. No. 3,611,803, Japanese Patent Application Laid-Open Publication No. 60-122324, International Application Publication Nos. W081/00312 and W093/22652.
It has also been known to, instead of dropping particulate material directly onto the detection plate from a vertically above position, guide the same along inclined chutes to the detection plate. Such a flow meter is seen in International Application Publication No. W093/22633 and Japanese Patent Publication No. H8-12091
FIG. 8 shows the arrangement proposed by Japanese Patent Publication No. H8-12091. The arrangement is such that one or more inclined buffer plates are provided between a discharge opening 103 in the lower portion of a particulate material supply device 102, which is below a hopper 101, and a detection plate 104. The particulate material dropping from the supply device 102 impinges upon the first one of the buffer plates, then slides down along the subsequent buffer plates, slides along the last buffer plate 105, and is finally dropped onto the detection plate 104. FIG. 8 illustrates only the final buffer plate 105 which is inclined in the same direction with the detection plate 104. The detection plate 104 is installed with its upper end located right below the lower end of the final buffer plate 105, and it has a detecting system or load cell 100 for detecting the vertical component of a force exerted to the detection plate 104.
The flow meter thus constructed functions as follows. (1) Thanks to the provision of the buffer plate 105, the particulate material is substantially constant in its position of dropping, indicated by an arrow 106, and direction of dropping, indicated by an arrow 107, with respect to the detection plate 104, even though the flow rate varies. That is, unevenness of the speed of the particulate material dropped from the supply device 102 is uniform. (2) The buffer plate 105 and the detection plate 104 have only a small difference between their inclining angles. Accordingly, the particulate material impinges onto the detection plate 104 with less impact, and then moves while it slides on the detection plate 104. When setting the inclining angle .theta.D of the detection plate 104 less than the inclining angle .theta.B of the buffer plate 105, a quasi-static force can be applied to the detection plate 104 according as the particulate material is moving thereon.
By the way, many conventional impact type flow meters use a cut-gate type particulate material supply device as shown in FIG. 9. The supply device is provided in its lower portion with a cut-gate 102 and opens and closes the discharge opening through rotary movement of the cut-gate. Therefore, there are caused a part A in which the material tends to stagnate, and a part C in which the material smoothly flows, depending on a degree of opening of the cut-gate 102. A boundary layer B is formed between the part A and the part C, and the thickness of the boundary layer B varies with the opening degree of the cut-gate 102. Change in the thickness of the boundary layer B causes the angle of repose of the stagnating part A to vary and provides a possibility that the stagnating part A will crumble at once. Thus, with the supply device of this type, the opening degree of the cut-gate 102 does not always coincide with the flow rate of the material, and there are cases where the accuracy in measuring the flow rate of the material is subject to detrimental affection.
Further, the flow meter shown in FIG. 8, because of its construction in which the plurality of buffer plates are arranged in a stair-like manner and the load cell 100 is situated below the detection plate 104, is large in the height h of the apparatus, thereby becoming large in its overall size.